This invention relates generally to an imaging lidar (light detection and ranging) system. More particularly, this invention relates to an imaging UV/visible fluorosensing and Raman lidar system having the ability to simultaneously measure temporally, spatially and spectrally resolved laser backscatter from on the land, on or beneath the surface of bodies of water and in the atmosphere.
There are numerous civilian and military applications which require or could benefit from the remote and non-destructive sensing and probing of the spectrally-dependent optical properties of a scene. Such applications include (1) detection and classification of oil spills and oil seepage on land and the ocean; (2) remotely measuring the atmospheric release of a pollutant or a target chemical such as a chemical associated with illegal drug production and chemical warfare agents (which might be monitored in a treaty verification control agreement or on a battlefield); (3) the measurement of sub-oceanic surface biogenic fluorescence spectra or differential reflectance spectral images in a complex scene to enhance object or substance detection; (4) measurement of wavelength dependent fluorescence decay laws and performance of spontaneous and stimulated Raman spectroscopy to measure such parameters as water temperature, sea salinity, water turbidity (due to gaseous or solid dispersements), subsurface chemical pollution as well as performance of vibrational spectral identification of hydrocarbons and target chemicals.
Prior art methods are known for the remote probing of the spectrally dependent optical properties of a scene. Such prior art uses either "passive interrogation" where the sensor system casts no light of its own upon the land, sea or atmosphere; or "active interrogation" wherein an intense narrow spectral bandwidth light source, such as a laser, probes the optical properties of the different media. Examples of such "active" systems are described in "Laser Remote Sensing" by Raymond M. Measures, published by John Wiley & Sons, Inc. (1984). In general, while these prior art "active" systems have the ability to perform measurements of temporally resolved spectral reflectance, fluorescence and Raman scattering, such prior art "active" systems are deficient in their inability to produce quantitative areal, volumetric, radiometric and spectrometric imagery of a scene with geodetic measurements. Examples of passive remote sensing systems are described in F. E. Hoge, R. N. Swift and J. K. Yungel, "Active-Passive Ocean Color Measurements: 2 Applications", Appl. Opt. 25 (1986) 48-57.
Sensor systems for remote detection and imaging of objects in a backscattering medium are known and described in, for example, U.S. Pat. Nos. 4,862,267, 4,964,721, 4,967,270, 5,013,917 and U.S. Ser. No. 565,631 filed Aug. 10, 1990, all of which are assigned to the assignee hereof and fully incorporated herein by reference. In general, these imaging lidar systems utilize one or more laser transmitters which generate short pulses of light and project these pulses down toward an object or target enveloped by a backscattering medium. One or more gated camera receivers detect the pulses of light reflected from the target after an appropriate time delay. These detected reflected pulses of light are then converted to a video image of the target.
While well suited for their intended purposes, the above-mentioned imaging lidar systems generally do not have the ability to perform measurements of temporally resolved spectral reflectance, fluorescence and Raman scattering. As discussed, there is a perceived need for such measurements; and therefore known imaging lidar systems are not adequate in this regard.